1. Field of the Invention
This invention relates to the field of additives, and, more specifically, to wood sizing agents for poly(vinyl chloride)-wood composites used as building materials for decking, railing, window lineals, roofing shingles, fencing, siding, furniture, and the like.
2. Description of Related Art
Wood-poly(vinyl chloride) (PVC) composites are materials that look like wood and are used on a large scale in the building industry because of their low-cost maintenance and resistance to biological degradation. Being a component of the composite material, wood is known to negatively affect mechanical properties, such as tensile strength, impact strength, or flexural strength. These properties can be improved by assuring good adhesion of the PVC to the wood particles by preventing the thermal degradation of the PVC.
Attempts to improve the adhesion of PVC to wood particles have been directed primarily to the use of compatibilizers, such as those listed in the following groups:
Unsaturated, epoxy, amino, thio-alkyl trialkoxysilanes:                U.K. Patent Application GB 2 192 397 A;        Kotka, B. V., et al., J. Vinyl Technol. 12:146-153 (1990);        Matuana, L. M., et al., Polymer Composites 19:446-455 (1998);        Rodriguez-Fernandez, O. S., et al., Proceedings ANTEC 2002 (2002).        
Isocyanates and polymeric isocyanates:                U.K. Patent Application GB 2 192 398 A;        Maldas, D., et al., J. Reinforced Plastics and Composites 8:2 (1990);        U.S. Pat. No. 6,248,813.        
Carboxylic acids, anhydrides and polymeric anhydrides:                Matuana, L. M., et al., Polymer Composites 19:446-455 (1998);        
Carboxylic acids:                Kotka, B. V., et al. Polymer Composites 11:84-89 (1990).        U.S. Pat. No. 6,210,792.        
Chlorinated polyethylene and polyvinyl chloride copolymers:                Guffey, V. O., et al., Proceedings ANTEC 2002 (2002).        European application No. 0046579        
Phenol-, melamine-, urea-formaldehyde resins:                Natow, M. et al., Plaste und Kautschuk 29:277-278 (1982);        Canadian Patent No. 763,000;        U.S. Pat. No. 4,594,372.        
Acrylonitrile, methacrylates, vinyl acetate, acrylicimide, styrene and acrylamide polymers and copolymers:                U.S. Pat. No. 6,210,792;        U.S. Pat. No. 5,981,067.        
The following types of stabilizers are listed in the literature for use in PVC-wood composites:
Organotin thioglycolates and laurates:                U.S. Pat. No. 5,981,067        U.S. Pat. No. 6,015,612;        U.S. Pat. No. 6,210,792;        Joo, Y. L., et al., Proceedings Intern. Polymer Processing XIV: 10-20 (1999);        Mengeloglu, F., et al., J. Vinyl & Additive Technol. 6:153-157 (2000).        
Tribasic lead sulfate, lead stearate:                U.S. Pat. No. 4,594,372        French Patent No. 2 514 773;        European Patent Application No. 0 284 058 A2;        Rusu, M., et al., Industria Usoara 30:504-508 (1983).        
Barium acetate:                Kotka, B. V., et al., J Vinyl Technol. 12:146-153 (1990);        Kotka, B. V., et al. Polymer Composites 11:84-89 (1990).        
Alkyltin reverse esters sulfides, alkyltin maleates, and complex mixtures of calcium and zinc carboxylates and/or acetylacetonates:                R. Bacaloglu, P. Kleinaluth, P. Frenkel, P. Reed, and C. Coursen, U.S. patent application Ser. No. 10/827,823, filed Apr. 20, 2004.        
U.S. Pat. No. 5,981,067 relates to a composite pellet comprising a thermoplastic polymer and wood fiber composite that can be used in the form of a linear extrudate or thermoplastic pellet to manufacture structural members. The fiber can be modified to increase compatibility. The polymer and wood fiber composite may contain an intentional recycle of a waste stream which can comprise adhesive, paint, preservative, or other chemical waste stream common in the wood-window or door manufacturing process. The initial mixing step before extrusion of the composite material insures substantial mixing and melt contact between molten polymer and wood fiber. The extruded pellet is said to comprise a consistent proportion of polymer, wood fiber and water.
U.S. Pat. No. 6,280,667 discloses polymer/wood fiber composite structural members that can be manufactured in an extrusion process engineered to produce materials that are said to be of high quality. The composite can be in a linear extrudate or pellet and can have a cross-section of any arbitrary shape, or can be a regular-geometric or of arbitrary-amorphous shape. The extruded material comprises a consistent proportion of polymer, wood fiber and water. During the extrusion, water is removed intentionally to dry the material to a maximum water content of less than about 10 wt-% based on the pellet weight. To make a structural unit, the pellet is introduced into an extruder apparatus wherein, under conditions of controlled mass throughput, shear, mechanical energy input, controlled temperature and pressure, the composite material is produced.
Godavarti, S., Proceedings ANTEC 2003:2044-2046 (2003) a method to monitor quality of wood fiber reinforced thermoplastics based on the free, unreacted acid in the composite.